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Learn about the difference between global and local scope.
Welcome back.
0:00
Now that you now to define and
call a function,
0:01
we have to expand our discussion a little
bit to talk about something called scope.
0:04
Scope refers to the visibility
of parts of our program.
0:08
Not all parts of a program can be
seen by other parts of our program.
0:12
This is really important to remember
when you're thinking about functions.
0:15
The code you write inside of a function
is only accessible inside that function.
0:19
That means if you assign a variable inside
a function, you can't use that variable
0:24
in another part of your program and
expect it to reference the same value.
0:28
This can be a little hard
to grasp without seeing it.
0:32
Let's jump into some code.
0:35
Okay, take a look at my workspace here.
0:37
You see we have a variable
assignment num=10.
0:39
Then you see a function set_num.
0:43
Inside the set_num function there's
another variable assignment.
0:47
Num=5 after the function definition
the program calls set_num.
0:50
What do you think will be printed
when this program is run?
0:57
Pause the video here.
1:00
Open up the attached workspace, and
run the file in the workspace terminal,
1:01
see what's printed, and
then come join me again.
1:06
All right, how did it go?
1:09
Were you a little surprised by
the value that was printed?
1:10
Let's break this down.
1:13
The variable assignment num
= 10 takes place inside
1:15
what is known as the global context,
or the global scope.
1:19
It's global because it's not
inside any other function,
1:23
it's at the highest level in the program.
1:26
Any other part of this program can see,
access, and
1:28
use this variable including the code
inside the set_num function.
1:32
So when the set_num function is called and
1:36
Python encounters the num = 5 variable
assignment, it doesn't reassign num, it
1:38
creates a new num that only exist inside
the local context of the set_num function.
1:44
That means that outside of set_num,
even if we've already called it, num will
1:50
always reference 10 until this reference
has changed in the global context.
1:54
Inside the set_num function however,
num will have a value of five.
1:59
Additionally, if we create
a variable inside set_num,
2:05
we can't access it
outside of that function.
2:08
I'll create a new variable inside
the function called letter, and
2:11
it'll reference the letter a.
2:14
Let's see what happens when I try to print
the letter variable outside of set_num.
2:21
I'm gonna save,
run this down in my terminal.
2:28
Okay, we're getting an error here.
2:37
A name error that says name
'letter' is not defined.
2:39
Well, that's because there is no letter
variable inside the global scope.
2:44
Letter only exists inside
the set_num function and
2:48
can only be accessed inside of it.
2:52
If we move our print statement
inside the function and try again,
2:54
we'll probably get a different result.
2:57
Now I'm gonna save and try it again.
3:03
Cool, it printed the letter a.
3:08
So now that you know a little bit
about global and local scope,
3:10
you might be wondering how you actually
get values and variables out of functions.
3:13
A variable's created inside a function,
in the local scope,
3:18
can't be seen in the global scope,
then what's the point.
3:21
Stay tuned to find out.
3:24
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